A fixation releasing device has conventionally been known. The fixation releasing device comprises a buoyant body and a weight connected by a connection device and configured to release connection between the buoyant body and the weight by a separation mechanism. There is provided an OBS (Ocean Bottom Seismograph), for example, configured to be installed on a sea floor or at the bottom of the ocean to carry out measurement in order to conduct a seismic survey by sinking the OBS onto the bottom of the ocean. In a seismic refraction survey to be conducted to study a mechanism of occurrence of an earthquake at the bottom of the ocean or for other purposes, an artificial seismic wave is generated, and the sound wave refracted at a boundary surface between respective strata under the ocean bottom is received by a large number of ocean bottom seismographs installed at the bottom of the ocean at predetermined distances, thereby carrying out measurement. The ocean seismograph thus used is formed by a combination of an ocean bottom seismograph body and an anchor (weight), and is sunk at the bottom of the ocean. The ocean seismograph body is a buoyant body including therein a sensor and other parts. The anchor is disposed under the buoyant body in order to moor the ocean seismograph body at the bottom of the ocean. After the measurement, a recovery operation of a body portion of the ocean seismograph is performed for data collection, device maintenance, or other purposes. The recovery operation is performed by operating a separation mechanism provided at a connection device configured to connect the buoyant body and the weight.
As the separation mechanism, there is a gunpowder method (disclosed in JP08-271291A (Patent Document 1)), an electric corrosion method (disclosed in JP2006-030124A (Patent Document 2)), etc. In the gunpowder method, an action of cutting a cable configured to connect a buoyant body and a weight with a cutting blade is triggered by explosion of gunpowder. In the electric corrosion method, a metal plate (such as a stainless plate) or a metal wire, configured to connect a buoyant body and a weight is electrically corroded forcibly to be cut. The buoyant body and the weight are thereby separated.